Permanent magnet compositions based on the rare earth (RE) elements neodymium or praseodymium or both, the transition metal iron or mixtures of iron and cobalt, and boron are known. Preferred compositions contain a large proportion of an RE.sub.2 TM.sub.14 B phase where TM is one or more transition metal elements including iron. A preferred method of processing such alloys involves rapidly solidifying molten alloy to achieve a substantially amorphous to very finely crystalline microstructure that has isotropic, permanently magnetic properties. In another preferred method, overquenched alloys without appreciable coercivity can be annealed at suitable temperatures to cause grain growth and thereby induce magnetic coercivity in a material having isotropic, permanently magnetic properties.
It is also known that particles of rapidly solidified RE-Fe-B based isotropic alloys can be hot pressed into a substantially fully densified body and that such body can be further hot worked and plastically deformed to make an excellent anisotropic permanent magnet. Thus, alloys with overquenched, substantially amorphous microstructures are worked and plastically deformed at elevated temperatures to cause grain growth and crystallite orientation which result in substantially higher energy products than in the best as-rapidly-solidified alloys.
As stated above, the preferred rare earth (RE)-transition metal (TM)-boron (B) permanent magnet composition consists predominantly of RE.sub.2 TM.sub.14 B grains with an RE-containing minor phase(s) present as a layer at the grain boundaries. It is particularly preferred that on the average the RE.sub.2 TM.sub.14 B grains be no larger than about 500 nm in the permanent magnet product.
While such hot working, e.g., die upsetting, produces individual magnets suitable for many purposes, in some applications it would be desirable to provide such a magnet with an integral, high strength metal backing plate. We perceive that such an assembly could be formed during hot work processing of the isotropic particles by employing a backing material to aid in the formation of anisotropic magnet bodies while simultaneously providing a bond between the anisotropic material layer and a high strength metal backing.
It is known to provide a metal backing for a rare earth metal-cobalt powder as shown in U.S. Pat. No. 4,076,561. However, the prior art does not disclose the use of a metal layer to aid in a desired crystallographic orientation of magnetically isotropic material with respect to a metal backing plate to produce a resultant anisotropic magnet body.